by Gary Boas
Shamanic rituals involving each of these have been with us for millennia. They are among the oldest and most widespread forms of healing known to humanity, cutting across cultures and spreading to the four corners of the Earth.
This universality suggests a biological basis for achieving a trance state. But for all the history of shamanism, for all its significance to the human experience, we actually know very little about the neural underpinnings of altered consciousness in the trance state.
Now, in collaboration with researchers from the Max Planck Institute and elsewhere, investigators with the MGH Martinos Center for Biomedical Imaging have for the first time explored this phenomenon.
The project was led by the Martinos Center’s Michael Hove(1). Hove collected the data with Johannes Stelzer while a fellow at Max Planck Institute and, after moving to MGH, conducted further analyses with the Center’s Koene Van Dijk.
Fifteen experienced shamanic practitioners from throughout Germany and Austria were invited to participate in experiments, which used the advanced technique functional Magnetic Resonance Imaging (fMRI). Imaging was performed with the shamans either entering into or remaining out of trance while listening to drumming.
The analyses revealed a great deal about connectivity in the shamans’ brains—that is, the functional links between regions of their brains—during trance.
The scientists noted, for example, increased connectivity in the posterior cingulate cortex, a major default network hub involved in internally directed thought, as well as in the insula and anterior cingulate cortex, two core control network regions. Co-activation of these areas points to the control network playing a role in maintaining an extended internally directed state during trance.
Just how important is drumming in shamanic rituals?
The investigators also saw during the trance state evidence of decreased connectivity in the auditory pathway of the brain. This suggests that the sound of repetitive drumming, which often accompanies shamanic rituals, is so predictable that it requires little additional processing and can be largely gated out.
This could explain—paradoxically, perhaps—why drumming is so commonly used to induce trance. Deliberate application of such a “predictable external stimulus” helps the shaman disengage from the external environment, Hove said. At the same time, it serves to extend the shaman’s internally directed state, thus facilitating the clarity and insight associated with the rituals.
About the Author
Gary Boas is the Senior Communications Manager, Martinos Center for Biomedical Imaging. Gary oversees all communications efforts and other writing and editing needs in this major biomedical research center based at Massachusetts General Hospital and affiliated with Harvard Medical School and MIT. These efforts include news writing, media relations, and internal and hospital-wide communications.
(1) Michael Hove, Harvard Medical School, Department of Psychiatry. Hove and colleagues published the findings online recently in the journal Cerebral Cortex.